Blizzards in New Zealand have grounded flights, closed roads and shut off power in what forecasters are describing as once-in-a-lifetime conditions.

The cities of Wellington and Auckland saw their first snow for decades after an Antarctic blast moved north from South Island at the weekend, with the cold snap predicted to continue until Wednesday.

MetService head forecaster, Peter Kreft, told the New Zealand Press Association: "It's a once in many decades event. We are probably looking at something like – in terms of extent and severity – maybe 50 years," he said.

Services across the country were disrupted on Monday, with electricity cut to thousands of homes in Wellington and north of Auckland. Schools, universities and courts were closed across much of the lower South Island.

Flights and mail delivery had to be cancelled as well.Police warned that the snow would freeze overnight and create unsafe driving conditions.

Residents took to the streets with cameras and cheers, enjoying the unusual conditions, while Wellington Zoo veterinarians took advantage by giving Happy Feet, the emperor penguin they found sick and starving on the west coast last June, a chance to enjoy the ice.

Stephen Fry, who is in Wellington filming The Hobbit, described the atmosphere on Twitter. "It's been an exciting day here in Wellington. Snow. That's unusual. NZ is same latitude as Melbourne so it's rare."